Rapamycin (also known as sirolimus), is a macrocyclic lactone produced by Streptomyces hygroscopicus. The structural formula of rapamycin is shown below:

Rapamycin is known for its use as a therapeutic for immunosuppression and for treating transplantation rejection, host vs. graft disease, autoimmune diseases, and diseases of inflammation, solid tumors, fungal infections, adult T-cell leukemia/lymphomas and hyperproliferative vascular disorders. Rapamycin is also useful in the treatment of Lymphangiolciomyomatosis (LAM). LAM is a rare lung disease found primarily in women that often affects other organs including lymph nodes and kidneys.
Rapamycin is available in the form of crystalline powder and is known to be insoluble in water. It is known to a skilled person that the transformation of the crystalline form of a low solubility drug to the amorphous form can significantly increase the solubility thereof which is also true for rapamycin. However amorphous rapamycin is extremely chemically unstable and is therefore not easily formulated into any pharmaceutical dosage form. The present invention overcomes the problems described above by providing stable spray-dried, particle formulations of rapamycin for pulmonary administration to a patient.